Shen Li, Wang Xuemin, Liu Heyuan, Li Xiyou
College of Science, China University of Petroleum (East China), Qingdao, 226580, China.
Phys Chem Chem Phys. 2018 Feb 21;20(8):5795-5802. doi: 10.1039/c7cp08313k.
Efficient singlet fission (SF) has been obtained in quinoidal bithiophene, end-capped with dicyanomethylene groups (QBT). However, QBT suffers from low triplet state energy [E(T)] because of its biradicaloid nature, which results in a great driving force for SF but also a large loss of energy during the SF process. This is not favorable for the application of SF in solar cells. Modifications to the molecular structure of QBT were performed to optimize the SF relevant excited state energy levels and its diradical character in the present study. This includes chalcogen replacement, the fusing of the heterocyclic ring between the two thiophene rings, and the introduction of side substituents. Detailed analysis focused on the correlation between the molecular structure of the QBT derivatives and their diradical character y, bond length alternation (BLA), molecular orbitals, and SF relevant excited state energy levels. The results show that electron-donating substituents, particularly groups introduced at the inner β-positions of the thiophene ring, can increase E(T) and reduce the energy loss of SF significantly under the premise of exothermic SF. These results would be beneficial to the development of new SF candidates for application in solar cells.
在由二氰基亚甲基封端的醌型联噻吩（QBT）中已实现了高效的单线态裂变（SF）。然而，由于其双自由基性质，QBT的三重态能量[E(T)]较低，这导致了SF有很大的驱动力，但在SF过程中也有大量的能量损失。这对SF在太阳能电池中的应用不利。在本研究中，对QBT的分子结构进行了修饰，以优化与SF相关的激发态能级及其双自由基特性。这包括硫族元素取代、两个噻吩环之间杂环的稠合以及侧链取代基的引入。详细分析聚焦于QBT衍生物的分子结构与其双自由基特性y、键长交替（BLA）、分子轨道以及与SF相关的激发态能级之间的相关性。结果表明，供电子取代基，特别是在噻吩环内β位引入基团，在SF放热的前提下，可以显著提高E(T)并降低SF的能量损失。这些结果将有利于开发用于太阳能电池应用的新型SF候选物。
